Since in rotary kilns the greater proportion of the heat energy has to be transmitted to the material to be treated by radiation, great demands are made on the temperature profile produced by the burner in the direction of the longitudinal axis of the kiln. This is aggravated by the fact that for reasons of heat economy the highest possible proportion of the combustion air should be delivered to the kiln system in the form of preheated secondary air from the cooling of the burnt material. Generally speaking this secondary air cannot be delivered via the burner.
The previously known burners for rotary kilns are therefore designed in such a way that the fuel is mixed together with the secondary air with the aid of the smallest possible proportion of primary air, which is usually taken from the ambient air. In order to stablise the flame an internal reverse flow is usually produced with the aid of swirlers or blockers.
In these known constructions rotating or diverging motions of a certain intensity are forced upon the free jets consisting of fuel and air and govern the intermixing with the secondary air. Without exception, flames produced in this way have the disadvantage that depending upon the intensity of the rotation or divergence a more or less large proportion of the fuel is thrown out of the actual flame and burnt in the secondary air stream, which results in a lowering of the density of energy of the flame or an increase in the specific volume of the flame.
In the previously known constructions strict limits are set on the production of short flames, since the intensification of rotation or divergence which this requires brings with it of necessity an increase in the internal reverse flow. This internal reverse flow takes up a certain space but does not increase the number of combustion reactions taking place per unit of volume. In combination with the increase in the proportion of fuel thrown out of the flame, this leads very rapidly to an undesirable increase in the diameter of the flame, which brings with it the danger that the flame will touch the refractory lining of the combustion chamber and the fuel.
The object of the invention, therefore, is to create a method and a burner for burning solid, liquid or gaseous fuel, particularly for rotary kilns, in such a way that throwing out of fuel particles is avoided, rapid and uniform intermixing of the fuel-primary air free jet with the secondary air is achieved as well as an early start and rapid progress of the combustion and thus a short flame is achieved.